Navigation with Signals and Constraints of Opportunity: Exploiting Unstructured Environments for State Estimation offers a conceptual framework for navigation and positioning using these sensors on the lines of standard control theory and dealing with navigation as state estimation in both indoor and outdoor environments. Using signals and constraints of opportunity, the book shows how geomagnetic field, topography (changes in the direction of g locally), landmarks, angles to celestial bodies, local acoustics and presence of magnetic fields, and changes in background radiation (radio signals, Wi-Fi, etc.) can be integrated for accurate geolocation in place, or in conjunction with, GPS to aid inertial navigation. Accelerometers, gyroscopes, cameras, magnetometers, microphones, and several other sensors are currently being produced in industrial scale, and as miniaturization advances, both price and portability are decreasing. The authors have created and integrated several sensors that could be incorporated in navigation systems, cellphones, or automated irrigation devices. In this book, the fundamental problem of navigation is stated and the use of signals of opportunity is detailed and integrated into an alternative navigation framework.